Alternating-current motor



(No. Model.) '3 Sheets-Sheet 1.

' v O. S. BRADLEY.

ALTERNATING CURRENT MOTOR.

'anvemhoz Charles Sfinzdley Wit Waxes AN DIEW B.GRAHAM.PHOTTUTHKLWASHHJEION. I) O (No Model.) 3 Sheets-Sheet 2. G. S. BRADLEY.ALTERNATING CURRENT MOTOR.

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3 Sheets-Sheet 3.

(No Model.) I

' G. S. BRADLEY.

ALTBRNATING CURRENT MOTOR.

No. 551,810. I Patented Dec. 24; 1895.

- 53 A4 em Wm I Q 13 Md/A ANDREW B GRAHAMPMDTO-LITHO.WASHINGTON.DC V 7'UNITED STATES PATENT OFFICE.

CHARLES S. BRADLEY, OF AV ON, NElV YORK.

ALTERNATlNG-CU-RRENT MOTOR.

SPECIFICATION forming part of Letters Patent No. 551,810, dated December24, 1895.

Application filed September 12, 1893. Serial No. 486,311. (No model.)

T0 at whom, it may concern.-

Be it known that I, CHARLES S. BRADLEY, a citizen of the United States,residing in Avon, in the county of Livingston and State of New York,have invented certain new and useful Improvements in Alternating CurrentMotors, of which the following is a specification.

This invention relates to polyphase alternating-current motors, itsobject being to dis pense with the resistance ordinarily employed in thesecondary circuit to vary the torque, and to dispense with any externalelectrical connections whatever for the secondary circuit, and yetpermit the motor to start with strong torque.

In carrying out the invention I make the primary element the fixedelement of the motor and mount the secondary element upon a shaftcarrying two or more series of contacts with which the terminals ofseveral secondary circuits may be brought into engagement by differentmodes of coupling to produce different degrees of magnetization on thesecondary element and thus prevent the secondary poles overpowering theprimary poles at low speeds.

In a prior application filed jointly by my- I self and Fred S. Hunting,Serial No. 475,586,

filed on or about the 20th day of May, 1893, was described a polyphasealternating-current motor in which the secondary element was wound withseveral groups of coils, the terminals of which were carried to anexternal coupling-switch by which they might be connected in variousrelations so as to oppose or assist one another in polarizing thesecondary element. In the construction therein described the primaryelement was made the revolving element of the motor, which necessitatedleading the polyphase currents to the primary circuits throughOOlltELCtdlllgS carried by the revolving shaft. Such contact-rings aredispensed with in my present invention.

The several features of novelty of the invention will be moreparticularly hereinafter described and will be definitely indicated inthe claims appended to this specification.

In the accompanying drawings, which illustrate the invention, Figure 1is a diagrammatic view of a motor embodying my improvements. Fig. 2 is aside elevation, partly in section, of such a mot-or; and Fig. 3 is adevelopment of the switch device carried by the revolving shaft, showingdiagrammatically the several circuits and the mode of connecting them invarious ways so as to vary the number of effective turns in thesecondary winding.

Referring first to Fig. 1, a b 0 represent the supply-wires of apolyphasc circuit, in this instance a triphase circuit. The primaryelementA of the motor will be fixed upon a suitable base and may bewound with an open or closed coil system. As shown the primary elementis wound with a closed circuit connected with the three supply-wires a bc, the winding being adapted to develop four progressive or rotatingpoles. This may be readily done by tapping the closed winding at sixequidistant points If t f if t if, and connecting the wire a of thetriphase circuit with points if and If, the wire I) with points i andIf, and the Wire 0 with t and t lVith this system of connections ifcurrent be supposed to be entering at any given instant on the wire a,and returning by Wires 1) and c, it will enter the winding at points Ifand 25* in multiple arc, and return to the main 1) at points i and If,and to the main 0 at points 25 and 23 thus developing four poles in thering-core inclosed in the primary winding. These four poles will have aprogressiye movement through the ring under the fluctuations of thetriphase current.

The secondary element B is mounted upon a shaft 0 so as to rotate withinthe primary element. This element is provided with two independentwindings X X X X, Y Y Y Y, relatively displaced on the ring-core so asto have induced therein secondary currents hav ing a quarter-phasedifference, and each circuit is composed of several sections, theterminals of which lead to brushes 1" 2 3 4; 5, &c., to 12 mounted uponan insulatingring D fixed to the shaft. Splined upon the shaft andadapted to slide thereon is an insulating-collar E provided with threecircumferential rows of contacts 6 c e ,(see Fig. 2,) any one of whichmay be shifted by means of the lever F into engagement with the contact-springs 1 2 3, &c. The shifting-lever F is provided with a suitablehandle and latch for looking it in different positions of adj ustment,and carries at its extremity a pin G entering a circumferential grooveformed in a bushing upon which the collar E is rigidly mounted. The twoindependent windings X, &c., and Y, &c., have in each quarter of thesecondary element, in the case of a four-po1e motor, as the present,several sets of convolutions having diiferent magnetizing values that isto say, different numbers of turns. For example, in each quarter of thering we will have three sets of convolutions in the X system, and threesets of convolutions in the Y system, as seen at X X X X and Y Y Y Y.

Of course for a motor having a larger or smaller number of poles thenumber of ringsections would correspondingly vary.

It will be seen that when the switch is adjusted so that any one of theseries of contacts e e 6 comes into engagement with the brushes 1 2 3,&c., two independent closed circuits will be formed on the secondaryelement. Taking, for example, the condition of adjustment illustrated inFig. 1, and start ing from brush 1, we will pass through the first groupof convolutions of X, thence reversely through the same group of Xthence directly through the same group of X thence reversely through thesame group of Xfithence to brush 7 a and contact-block '7, and by fixedconnection 011 the under side of sleeve E to contact-block 2 and brush2, thence to secondsections of X X X X, and through it similarly to thefirst section, thence to contact-brush S and contact-block 8, and byfixed connection to contact-block 3 and brush 3 to the third section ofX X X X thence to contact-brush 9 and contact-block 9, and by fixedconnection back to the point of starting through contact-block 1 tobrush 1. By tracing the system of connections for the winding Y Y Y Y wewill find a similar arrangementthat is to say, the several sections ofeach winding X X X X and Y Y Y Y will be connected by the brushes andcontactblocks in such a way as to form two inde pendent closed circuits,and inasmuch as the tWo circuits are relatively displaced a distance onthe ring-core to develop induced currents having a quarter-phasedifference, the two induced circuits will co-operate to produce amagnetization in the secondary element which will not fluctuate greatlyfor any given speed of the motor. This degree of magnetization may,however, be varied at constant speed by shifting the sleeve E so asbring another group of contacts-say c -into engagement with the brushes1 2 3, &c.

In the system hereinabove traced the coils are all coupled in such away'as to assist one another in magnetizing the secondary element, butby suitably connecting the different series of contacts 6, 6 or 6 someof the sections of X and Y maybe made to oppose the magnetizing effortdeveloped by the other sections, and thus vary the degree ofmagnetization induced in the secondary element. This will be betterunderstood by an examination'of Fig. 3, where it will be seen, when thebrushes 1 2 3, &c., bear upon. contactblocks 6, the coils of winding Xand Y will be connected in two independent circuits in such a way as toassist one another. lVhen, however, the brushes 1 2 3, &c., bear uponseries 8 we will then, starting from brush 1, go through the section soin the direction of the arrow into brush 7, thence to contact-block 7 of6 thence by fixed connection to contactblock 9 of 6 and by brush 9through 00 in a reverse direction into brush 3, contact-block 3 of 6thence by fixed connection to contact block 8, and by brush 8 throughsection in a direction indicated by the arrow, and thence by brush 2 tocontact-block 2, and by fixed connection to contact-block 1 back tobrush 1, which was the point of starting. Thus it will be seen that thesections 00 00 co-operate in magnetizing the secondary element and areopposed by section or. By tracing sections y 3 11 of winding Y it willbe seen that a similar condition of affairs will exist. By adjusting theseries of contacts 6 into engagement with the contact-springs two of thesections may be made to oppose the larger one. Thus if we have in theseveral sections a number of convolutions in the proportion of one,three an d five,as illustrated in Fig. 1,we may have three differentmagnetizing values by forming three series of contacts, so that in theseveral positions of adjustment we will have 5|3+1 9 effectiveconvolutions,or 5(3+1):1 effective convolution, or 5+1- 3 3 effectiveeonvolutions. Thus when starting the motor into operation the switchwill be adjusted so that the second condition will be brought about anda low magnetizing value will be given to the coil system on thesecondary element; and this is as it should be, for the reason that whenstarting an induction motor into operation the slip is so great thatstrong induced currents are developed, and if the winding has a lowmagnetizing value a better co-operation of the poles of the primary andsecondary elements will result. As the motor rises in speed the switchwill be shifted by means of the lever F,-so that the third condition isdeveloped-that is to say, there will be a larger number of effectiveturns, which is as it should be, for the reason that the rotary elementhas now risen in speed so that the degree of slip is less, andconsequently a lower degree of induction exists. A final adjustment maythen be made by which all of the turns will be rendered effective, andas the degree of slip is comparatively slight at high speed, the weakerinduced current will be thus enabled to maintain the magnetization ofthe secondary element at a value which will develop strong torque.

It will thus be seen that the motor maybe given a strong torque whetherstarting or at medium speed or at full speed, by simply shifting thelever F so as to bring the proper group of contacts into co-operativerelation to the terminals of the secondary element.

Having thus described my invention, what I claim as new, and desire tosecure by Letters Patent, is

1. An alternating current induction motor comprising a primary elementand a revolving secondary element carrying a sliding switch cooperatingwith two or more series of 0011- tacts for varying the number ofeffective turns on the secondary winding.

2. An alternating current induction motor comprising a fixed primaryelement and a movable secondary element carrying a switch, and two ormore series of contacts for grouping the secondary windings to vary thenumber of eii'ective turns on the secondary winding.

3. An alternating current induction motor comprising a fixed primaryelement, a revolving secondary element provided with a sectionalwinding, the several sections having different numbers of turns, arevolving switch carried by the revolving shaft having two or moreseries of contacts cooperating with the section terminals to vary thenumber of effective turns, and means for shifting any set of contactsinto engagement with the terminals.

4. An alternating current induction motor comprising a fixed primaryelement, and a revolving secondary element provided with a plurality ofindependent sectional windings relatively displaced to producedifferential phase induced currents, and a sliding switch mounted on therevolving element for coupling the several sections of the windings indifferent relations to vary the number of effective turns.

5. An alternating current induction motor comprising a fixed primaryelement having a polyphase winding to develop a shifting or revolvingmagnetic field, a revolving secondary element provided with a pluralityof independent sectional windings relatively displaced to producedifferential phase induced currents, two or more series of contacts forgrouping the several sections to vary the number of effectivemagnetizing turns, and means for bringing any set of contacts intoengagement with the terminals of the sectional windings.

(3. An electric motor having a sectional winding on its revolvingelement, a switch fixed to the element for varying the number ofeffective turns in said winding, and means for adjusting the switchduring its revolution.

In testimony whereof I have hereunto subscribed my name this Sth day ofSeptember, A. D. 1893.

CHARLES S. BRADLEY.

\Vitnesses:

J. D. (Mason, CYRUS ALLEN.

